This invention relates to electronic signalling and indicating devices, and more particularly, to such devices employed in conjunction with a meter or instrument to provide electronic outputs indicative of meter conditions.
In many applications it is desirable to have electric signal indications of the condition of a conventional, mechanical-movement meter. For example, certain devices monitored by a meter are required to operate within limits, generally high and low limits. Should the device fall outside of the desired limits, it is necessary to provide an indication of this undesirable condition. This is most easily accomplished by an electronic switch which activates a preventative or alarm device. Furthermore, it is often desirable to monitor the condition of a meter from a long distance, such as with remote and automatic control applications where visual readings are impossible. In these situations, it is necessary to provide an electrical communication link to indicate the meter condition.
Most conventional meters are designed for providing only visual indications. Since these types of meters are unsatisfactory for many of the foregoing applications, it is necessary that additional apparatus be incorporated to provide electrical indications. Such apparatus should be easily adaptable to a conventional instrument. Since many instrument movements are of a delicate mechanical design, and thereby easily affected by external forces, the apparatus should not apply any force to the meter movement so as to give false or inaccurate readings. It is also desirable that the meter signalling apparatus have provisions for providing a plurality of outputs, snce it is often desirable to monitor a number of different operating conditions. To accomplish this multiple condition monitoring, the electronic circuitry should be as simple as possible, and should make use of conventional power sources to simplify use of the device. Accordingly, it is a general object of this invention to provide an electronic meter signal which achieves the foregoing requirements.
It is an object of this invention to provide an electronic meter signalling device which may be combined with a conventional mechanical indicating instrument.
It is an object of this invention to provide an electronic meter signalling device which does not adversely affect the indications or operation of a mechanical indicating instrument.
It is another object of this invention to provide an electronic meter signalling device which provides at least one additional signal other than those signals provided at different operating conditions of the conventional instrument.
It is a further object of this invention to provide an electronic meter signalling device of simple construction which employs a conventional power supply to simplify its combination with a conventional mechanical instrument.
To achieve these and other objects, a preferred embodiment of the invention comprises a capacitive coupling means retained adjacent the scale of a conventional mechanical-movement meter or gauge and an electronic discriminating circuit used in conjunction with the capacitive coupling means. The capacitive coupling means employs an indicator of the instrument to form a capacitive-coupled link between limit electrode means and the electronic discriminating circuitry. A capacitive link causes no forces, inaccuracies, or false readings to be introduced into the movement of the instrument. Various limit electrode means are positioned at preselected points along the scale of the instrument and as the indicator comes in proximity with each limit electrode means, an electric signal is transmitted from the limit electrode means through the indicator to the electronic circuitry. The electronic circuitry distinguishes each of these introduced signals and provides outputs indicative of the preselected conditions of the indicator. Furthermore, the electronic circuitry distinguishes between the signals generated and provides additional outputs indicative of other conditions of the instrument.